1. Field of the Invention
The present invention relates to phosphor blends for wavelength conversion. More specifically, the present invention relates to a phosphor blend for wavelength conversion capable of producing various colors, a phosphor blend emitting white light with reduced yellowing and a high color rendering index, and a white light emitting device using the white light emitting phosphor blend.
2. Description of the Related Art
Generally, phosphors for wavelength conversion are materials used for converting light at particular wavelengths emitted from various light sources to light at desired wavelengths. Among various light sources, light emitting diodes are particularly advantageous for backlights in liquid crystal displays (LCDs), automotive illuminators, and household illuminators in terms of their low driving power and superior light emission efficiency. For these reasons, phosphor materials have recently been spotlighted as key materials for manufacturing white LEDs.
Conventional white light emitting devices are predominantly manufactured by applying a yellow phosphor to a blue LED. More specifically, YAG(Y3Al5Gd12):Ce as a yellow phosphor is applied to the light-emitting surface of a blue LED, including a GaN/InGaN active layer, to convert a portion of blue light to yellow light, and then the converted yellow light is combined with the unconverted portion of the blue light to produce white light.
However, as the operation temperature increases after long-term use, the problem of yellowing becomes more serious.
Further, conventional white light emitting devices composed of a YAG:Ce phosphor and a blue LED have the disadvantage of poor color rendering properties. That is, as can be seen from the graph shown in FIG. 1, the wavelengths of white light emitted by the yellow phosphor are distributed in the blue and yellow wavelength ranges only. Accordingly, the conventional white light emitting devices show poor color rendering properties and thus there is a limitation in the production of the desired natural white light.
On the other hand, conventional phosphor materials for wavelength conversion provide colors of light emitted from particular light sources and colors of output light at particular wavelengths, and thus their color distributions are very limited. Consequently, there is a limitation in the application of conventional phosphor materials to colors of light emitted from various light sources and/or various colors of output light in order to meet the needs of users.
Thus, there exists a need in the art for a phosphor blend emitting white light with a high color rendering index and reduced yellowing, and a white light emitting device using the phosphor blend. Further, there is a need for a phosphor blend capable of ensuring a broad range of color distribution.